1. Field of the Invention
The present invention relates to a drying apparatus, particularly to the drying apparatus suitable for a drying process in a manufacturing line of a presensitized plate (hereinafter PS plate).
2. Background Arts
In a PS plate manufacturing line, an aluminum web is coated with a coating liquid and dried in a dryer booth. Then, a coated aluminum web is cut into a predetermined size to obtain a PS plate.
A drying apparatus for drying a coated surface of the aluminum web by blowing hot air thereto is well known (for example, cited in Japanese Patent Laid-Open Publication Number 2003-98685). The coating liquid used for the PS plate of such as conventional type or digital-corresponding type (called CTP) are different depending on the types of the PS plate, and a web temperature for drying the coated surface is varied widely in accordance with properties of the coating liquids. Accordingly, it requires a wide range of temperature (for example, about 50-200° C.) for drying air corresponding to all types of the PS plate.
In the drying apparatus for the PS plate cited in Japanese Patent Laid-Open Publication Number 2003-98685 above set forth, steam is supplied to a heat exchanger from a boiler for generating hot air. High pressure steam is required to gain hot air; for example, in order to generate hot air of 200° C., 2 Mpa (20 kg/cm2) of high pressure steam is required. Meanwhile, in order to generate air of 50° C., it is required to reduce the steam or steam pressure. The steam is reduced by providing a plural of steam controlling valves in parallel with each other, while steam pressure is reduced by piping via a decompression control valve. However, it is hard to adjust the temperature of drying air for drying the PS plates, which requires that the temperature of drying air is controlled to be a predetermined temperature with high accuracy (±1° C. of error).
Equipments such as a high pressure boiler and a high pressure piping are necessary to supply the heat exchanger with steam such that the heat exchanger send hot air in a wide range of 50-200° C. into the dryer booth in the PS plate manufacturing line, and accuracy of the temperature of hot air needs to be maintained corresponding to the change of the amount of hot air. However, it results in rising of costs for equipments and maintenance. An oil heater and an electronic heater may be alternatively used to heat air for drying the aluminum web, or a heat roll and a coil may also be used to heat the aluminum web directly by induction heating. Nevertheless, the problem of raising costs for equipments and maintenance is still remained.